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witnet-ethereum-bridge

witnet-ethereum-bridge is an open source implementation of a bridge from Ethereum to Witnet. This repository provides several contracts:

  • The Witnet Bridge Interface(WBI), which includes all the needed functionality to relay data requests and their results from Ethereum to Witnet and the other way round.
  • UsingWitnet, an inheritable client contract that injects methods for interacting with the WBI in the most convenient way.
  • BlockRelay, a contract that incentivizes secure relaying of Witnet blocks into Ethereum so that Witnet transactions can be verified by the EVM.

The WitnetBridgeInterface contract provides the following methods:

  • postDataRequest:

    • description: posts a data request into the WBI in expectation that it will be relayed and resolved in Witnet with a total reward that equals to msg.value.
    • inputs:
      • _dr: the bytes corresponding to the Protocol Buffers serialization of the data request output.
      • _tallyReward: the amount of value that will be detracted from the transaction value and reserved for rewarding the reporting of the final result (aka tally) of the data request.
    • output:
      • _id: the unique identifier of the data request.

  • upgradeDataRequest:

    • description: increments the rewards of a data request by adding more value to it. The new request reward will be increased by msg.value minus the difference between the former tally reward and the new tally reward.
    • _inputs:
      • _id: the unique identifier of the data request.
      • _tallyReward: the new tally reward. Needs to be equal or greater than the former tally reward.

  • claimDataRequests:

    • description: claims eligibility for relaying the data requests specified by the listed IDs and puts aside the potential data request inclusion reward for the identity (public key hash) making the claim.
    • inputs:
      • _ids: the list of data request identifiers to be claimed.
      • _poe: a valid proof of eligibility generated by the bridge node that is claiming the data requests.

  • reportDataRequestInclusion:

    • description: presents a proof of inclusion to prove that the request was posted into Witnet so as to unlock the inclusion reward that was put aside for the claiming identity (public key hash).
    • inputs:
      • _id: the unique identifier of the data request.
      • _poi: a proof of inclusion proving that the data request appears listed in one recent block in Witnet.
      • _index: index in the merkle tree.
      • _blockHash: the hash of the block in which the data request was inserted.

  • reportResult:

    • description: reports the result of a data request in Witnet.
    • inputs:
      • _id: the unique identifier of the data request.
      • _poi: a proof of inclusion proving that the data in _result has been acknowledged by the Witnet network as being the final result for the data request by putting in a tally transaction inside a Witnet block.
      • _index: the position of the tally transaction in the tallies-only merkle tree in the Witnet block.
      • _blockHash: the hash of the block in which the result (tally) was inserted.
      • _result: the result itself as bytes.

  • readDataRequest:

    • description: retrieves the bytes of the serialization of one data request from the WBI.
    • inputs:
      • _id: the unique identifier of the data request.
    • output:
      • the data request bytes.

  • readResult:

    • description: retrieves the result (if already available) of one data request from the WBI.
    • inputs:
      • _id: the unique identifier of the data request.
    • output:
      • the result of the data request as bytes.

The BlockRelay contract has the following methods:

  • postNewBlock:
    • description: post a new block into the block relay.
    • inputs:
      • _blockHash: Hash of the block header.
      • _drMerkleRoot: the root hash of the requests-only merkle tree as contained in the block header.
      • _tallyMerkleRoot: the root hash of the tallies-only merkle tree as contained in the block header.
  • readDrMerkleRoot:
    • description: retrieve the requests-only merkle root hash that was reported for a specific block header.
    • inputs:
      • _blockHash: hash of the block header.
    • output:
      • requests-only merkle root hash in the block header.
  • readTallyMerkleRoot:
    • description: retrieve the tallies-only merkle root hash that was reported for a specific block header.
    • inputs:
      • _blockHash: hash of the block header.
    • output:
      • tallies-only merkle root hash in the block header.

The UsingWitnet contract injects the following methods into the contracts inheriting from it:

  • witnetPostDataRequest:

    • description: call to the WBI's postDataRequest method to post a data request into the WBI so its is resolved in Witnet with total reward specified in msg.value.
    • inputs:
      • _dr: the bytes corresponding to the Protocol Buffers serialization of the data request output.
      • _tallyReward: the amount of value that will be detracted from the transaction value and reserved for rewarding the reporting of the final result (aka tally) of the data request. that is destinated to reward the result inclusion.
    • output:
      • _id: the unique identifier of the data request.

  • witnetUpgradeDataRequest:

    • description: call to the WBI's upgradeDataRequest method to increment the total reward of the data request by adding more value to it. The new request reward will be increased by msg.value minus the difference between the former tally reward and the new tally reward.
    • inputs:
      • _id: the unique identifier of the data request.
      • _tallyReward: the new tally reward. Needs to be equal or greater than the former tally reward.

  • witnetReadResult:

    • description: call to the WBI's readResult method to retrieve the result of one data request from the WBI.
    • inputs:
      • _id: the unique identifier of the data request.
    • output:
      • the result of the data request as bytes.

Known limitations:

  • block relay is centralized at the moment (only the deployer of the contract is able to push blocks). In the future incentives will be established to decentralize block header reporting.
  • verify_poe is still empty. Proof of eligibility verification trough VRF should be implemented.

Usage

The UsingWitnet.sol contract can be used directly by inheritance or by instantiating it:

pragma solidity ^0.5.0;

import "./UsingWitnet.sol";

contract Example is UsingWitnet {

  uint256 drCost = 10;
  uint256 tallyReward = 5;
  bytes memory dr = /* Here goes the data request serialized bytes. */;

  function myOwnDrPost() public returns(uint256 id) {
    id =  witnetPostDataRequest.value(drCost)(dr, tallyReward);
  }
}

License

witnet-ethereum-bridge is published under the MIT license.